The Dallas Floodway needs more than half a billion dollars' worth of work -- a massive price tag that could cost Dallas City Hall more than $185 million.

According to a feasibility study released today by the U.S. Army Corps of Engineers, the Trinity River near downtown Dallas should be moved -- again -- in order to restore an aquatic ecosystem decimated by the channelization of the 1920s, as well as help accommodate the long-planned six-lane toll road the city wants to build between the levees. Says the report, restoring the Trinity to its "historic natural meandering" will cost more than $321 million.

On top of that, says the report, the floodway needs $257 million worth of work intended to mitigate the risk of flooding inside and outside the levees, where the study says there's some $12 billion in development at risk from flooding. Among the items on the Corps' to-do list: extend some pump-station outfalls and raise the levees, for starters.

The feds are giving the city some credit for taking early preventative steps that include sinking $38 million into the Baker Pump station near Sylvan Avenue and Irving Boulevard, and as well as a redo of the ancient Able Pump Station that's supposed to keep the city center dry. That knocks about $50 million off the original $579 million price tag in the Corps' new feasibility study.

Nevertheless, says Dallas City Council member Scott Griggs, $529 million is still "a staggering amount of money. And when it comes to flood control, we have a lot farther to go than anyone dreamed of."

The feds' portion of the $529-million price tag will come from Congressional appropriations. The feasibility study is just the first step toward that path.

"It's a huge cost," says Rob Newman, the Corps' director of the Trinity River Corridor Project. "But the takeaway for me is flood risk management, ecosystem restoration and recreation can work together. Right now, the flood risk management is out there, but nothing else is. It's a lot of wasted open space. Bringing people to the river, adding wildlife to the river, is a real asset to the city of Dallas. If you analyze everything together and work through it, you can turn something that's wasteland into something valuable for Dallas and the nation. But it's a big cost, because we're talking about a major river."

The city will pay for its $185 million portion out of upcoming bond programs or with private donations, says assistant city manager Jill Jordan, who oversees the Trinity River Corridor Project at city hall.

"At this point the Trinity is like all the other parks: We'll work on it bond program by bond program, and by the time we finish Phase 1 of the lakes it will be time to plan the next bond program," she says. "I would not imagine we'll put all of the channel remediation work into one program. So it could be phased, and we'd do little bits of it over time. As we develop future bond programs -- not only the one in 2017 but the one four years after that and into the future -- we'll take off little chunks, and we'll time it with development activities."

As far as the city of Dallas is concerned, the 134-page draft feasibility study and an accompanying 632-page environmental impact statement are "good news," says Jordan.

"This is another milestone on the path to getting our record of decision and our permission from the Corps to begin the construction of the Balanced Vision Plan." says Jordan, referring to the 2003 plan that ties together flood protection, recreational amenities, transportation projects, environmental restoration and economic development between the levees.

"We've got good news on the flood control, and the idea for having the channel meander and be more natural-looking comes from the Balanced Vision Plan," she says. "We are glad the Corps embraces that."

The release of the Corps' documents comes less than a week before the final public hearing concerning the so-called Trinity Parkway, the nine-mile high-speed toll road along the east levee of the Trinity River intended to connect Interstate 45/U.S. 175 with the Interstate 35E and State Highway 183 merger. A According to the final environmental impact statement released by the Federal Highway Administration, the city ultimately has two options among several studied: either build the road between the levees, or do nothing.

The Corps' feasibility study says its "Recommended Plan assumes the Trinity Parkway is built in the Floodway."

"Everything can be done," he says. "It's technologically feasible to do it, and we're working on the environmental portion, and it looks like it'll work and improve the habitat." But, he reminds, the Corps won't issue its final record of decision until December of this year.

Newman says there's actually not a lot of work left to be done to the levees -- maybe $10 million worth, which will toward raising "multiple low spots" by one or two feet. That dirt will be taken out of what's intended to become the West Dallas Lake east of Westmoreland Road.

There are still a handful of pump stations, among them Able and Charlie and Delta, whose capacity needs to be upgraded; most of them are decades old. "And even the ones from the '50s were probably used pump stations when we took them," says Newman.

"That's has the biggest risk to the levee system, digging down 30 feet," he says. "The reason it was straightened was because it was a bypass channel in the '20s, when you didn't think about ecosystem restoration. The Corps back then wasn't real environmental friendly."

Dallas residents first OK'd the Trinity River Corridor Project in 1998, with a vote authorizing what was at the time the city's largest bond package: $246 million. Sixteen years later, there are more bond packages on the horizon, and more after that.

"Back in 1998 we thought we were going to be getting the project done all at one time," says Jordan. "Well, that's not how it's going to be. Just like we have Fair Park or White Rock Lake, we're always working on it. The Trinity's just going to be like that."